1. Technical Field of the Invention
The present invention relates to a valve train system drive device for an internal combustion engine, and to an engine incorporating the valve train system drive device.
2. Background Art
Conventionally, the concept of a valve train system drive mechanism, that is, a device that transmits the driving force of a crankshaft to an overhead-cam type of valve train system via an idle gear for an internal combustion engine, is known (refer e.g. to Japanese Patent Publication 2006-183623, also published as US pub. 2006/0137636). In the engine disclosed in Japanese Patent Publication 2006-183623, an idle shaft supports an idle gear thereon, and respective ends of the idle shaft are supported by a boss part on a side surface of a crankcase, and by a boss part on a side surface of a crankcase cover. In addition, the idle shaft is fastened to a holder member fastened and fixed to the crankcase cover, and is thereby prevented from rotating.
However, in the above-described known valve train system drive mechanism for an internal combustion engine, a separate holder member is required on the crankcase cover in order to support the idle shaft. Therefore, this known system has problems in respect to size reduction, weight reduction, and simplification of the engine.